1. Field of the Invention
The present invention relates to a chair, more particularly to a chair with a seat that is slidable relative to a seat base for synchronously actuating a footrest and a backrest.
2. Description of the Related Art
Referring to FIGS. 1 and 2, a conventional chair is shown to include a seat 11, a footrest 13 disposed frontwardly of the seat 11, a backrest 12 disposed rearwardly of the seat 11, a front linkage unit that interconnects the footrest 13 and the seat 11, and a rear linkage unit that interconnects the backrest 12 and the seat 11. A control unit 14 interconnects the front and rear linkage units, and includes an operating lever exposed outwardly from the seat 11. Turning of the operating lever in clockwise and counterclockwise directions results in inclination adjustment of the backrest 12 and extension and retraction of the footrest 13 relative to the seat 11.
One drawback of the aforementioned conventional chair is that adjustment of the backrest 12 and the footrest 13 relative to the seat 11 can only be conducted by operating the operating lever, thereby inconveniencing the user.
Therefore, the object of this invention is to provide a chair having a backrest and a footrest, which can be adjusted relative a seat merely by virtue of movement of the body weight of a seated person so as to eliminate the aforementioned drawback associated with the prior art.
Accordingly, a chair of the present invention includes: a seat base having left and right sides, and front and rear ends; a slidable seat mounted slidably on the seat base; a backrest disposed rearwardly of the seat base, and having a lower end; a footrest disposed frontwardly of the seat base; and a front linkage unit interconnecting the seat base and the footrest, and including a pair of parallel linkage mechanisms disposed at the left and right sides of the seat base, respectively. Each of the linkage mechanisms includes a pair of rear links with front and rear ends, and a pair of front links with front and rear ends. The front ends of the front links are pivoted to the footrest. The rear ends of the front links are respectively pivoted to the front ends of the rear links. The rear end of one of the rear links is pivoted to the seat base. The rear end of the other one of the rear links is pivoted to the slidable seat so as to permit folding and unfolding of the linkage mechanisms, which, in turn, results in frontward and rearward movement of the footrest relative to the seat base. A rear linkage unit interconnects the seat base and the backrest, and includes a pair of crank mechanisms disposed at the left and right sides of the seat base, respectively. Each of the crank mechanisms includes a frame, a crank, a lever, and a coupler. The frame is fixed on and projects outwardly and rearwardly from the rear end of the seat base. The crank is fixed on and projects outwardly and downwardly from the lower end of the backrest, and is pivoted to the frame. The lever is pivoted to and projects rearwardly and downwardly from the frame. The coupler is interposed between the crank and the lever, and has two opposing ends respectively pivoted to the crank and the lever so as to permit co-swinging of the crank, the lever and the coupler relative to the frame when the seat slides frontward and rearward relative to the seat base and so as to permit inclination of the backrest relative to the seat. A pair of auxiliary links are disposed at the left and right sides of the seat base, respectively. Each of the auxiliary links extends between and is connected pivotally to the seat base and the lever so as to prevent disengagement between the slidable seat and the seat base when the slidable seat slides on the seat base.